1. Technical Field of the Invention
The present invention generally relates to telecommunications network equipment. More particularly, and not by way of any limitation, the present invention is directed to an integrated line inductor and line feed resistor arrangement used in network equipment.
2. Description of Related Art
Subscriber Line Interface Circuits (SLICs) are employed to provide an interface between a low voltage signal path in a telephone central office (CO) and a high voltage telephone subscriber line. The SLIC provides functions such as off hook detection, ringing signaling generation and battery feed to the subscriber line. The subscriber line consists of a telephone transmission line, including two conductors referred to as A and B or tip and ring (T/R); and the subscriber telephone equipment coupled across the tip and ring conductors. The subscriber line and the subscriber telephone equipment are also referred to as a subscriber loop.
The SLIC provides power from the telephone CO, or a remote office, to the subscriber line in response to a received battery voltage. The battery voltage is a DC voltage supplied to the SLIC to power the SLIC and the subscriber line. The battery voltage has a value generally in the range of −20 to −60 VDC. A typical value of the battery voltage can be about −48 VDC. The SLIC supplies a DC current at an operating DC voltage to the subscriber line in order to source power to the telephone circuitry such as a digital keypad. Superimposed on the DC current are AC signals of audio frequency by which information is conveyed between the subscriber and the CO. The battery voltage source is generated at the CO by a depletable energy source device such as a battery or by a DC generator.
In Digital Subscriber Line (DSL) applications provided to subscribers by Competitive Local Exchange Carriers (CLECs) or local telephone companies, each SLIC is coupled to the T/R line by a ceramic film resistor and line inductor which provide line feed resistance and low pass filtration, respectively. FIG. 1 (Prior Art) depicts an existing line inductor and line feed resistor arrangement 100 coupled to a Subscriber Line Interface Circuit (SLIC) and tip and ring (T/R) line. SLIC 102 is coupled to a pair of ceramic film resistors 104 and 106. The ceramic film resistors 104 and 106 are able to withstand high temperatures while offering a predetermined resistance, typically around 30 Ω, to current. A pair of line feed inductors 108 and 110 are coupled to the ceramic film resistors 104 and 106 and the T/R line. Whereas the existing arrangements have been employed in various network equipment applications, they are not without limitations, however. The ceramic film resistors are expensive, thereby adding to the overall cost structure of network equipment. Furthermore, matching the resistance of the ceramic resistors and the line feed inductors has proved to be difficult. The ceramic resistors must have a matched resistance within 0.1%. Hence, a need exists for a line inductor and line feed resistor arrangement that provides matched resistance as well as acceptable failure modalities when tested accordingly to certain GR-1089 tests. Additionally, a need exists for such a system and method to be inexpensive and require a minimum amount of board space.